A polarizing plate is ordinarily produced by sticking a film having, as a main component, cellulose triacetate as a transparent protective film on each side of a polarizing film in which iodine or a dichroic dye is allowed to be absorbed in vinyl alcohol in an alignment manner. Cellulose triacetate which has such characteristics as a high toughness, a high fire retardancy and a high optical isotropy (low retardation value) has widely been used as a transparent protective film for the polarizing plate.
A liquid crystal display device has a polarizing plate and a liquid crystal cell. At present, in a TFT liquid crystal display device of TN mode which is a main stream of the liquid crystal display device, as described in JP-A-8-50206, by interposing a optical compensatory sheet (retarder film) between the polarizing plate and the liquid crystal cell, the liquid crystal display device having a high display quality has been realized. However, in such method as described above, there is a problem in that the liquid crystal display device itself becomes thick and the like.
Against this method, JP patent application number 1-68940(published as JP-A-2-247602) discloses that a front face contrast can be enhanced by using an ellipsoidal polarizing plate in which one face of a polarizing film has an optical compensatory sheet and the other face of the polarizing film has a protective film, without increasing thickness of the liquid crystal display device. However, the optical compensatory sheet according to JP-A-2-247602 is likely to generate a phase difference derived from a strain caused by heat or the like and, accordingly, it is found that there is a problem in that a leakage of light occurs.
Against the problem of the phase difference derived from the strain, in JP-A-7-191217 and EP 0 911 656, techniques in each of which an optical compensatory sheet produced by applying an optical anisotropic layer having a discotic compound on a transparent support is used as it is as a protective film of the polarizing plate are described. It is described therein that the problem can be improved by these techniques without increasing the thickness of the liquid crystal display device.
However, even by these techniques, it has not been sufficient to allow hue to be neutral gray.
In the liquid crystal display device using the polarizing plate in which the optical compensatory sheet and the polarizing film are unified, although a viewing angle is wide, an improvement of the hue is not sufficient and, accordingly, there is a problem in that a leakage of light is generated.